Hydraulic stick control



May 12, 1953 HFUQ .J. D. M KELLAR ET AL HYDRAULIC STICK CONTROL Filed Feb. 5, 1949 INVENTORS JOHN D. mzaua BY 20M4LD (RANDALL ,4 t t a r n e U Patented May 12, 1953 JohaDrMeKeu-ar iid nanale lai oranaeir" os Angeles,'-Galif&,-'-rassignors to Northrop Aircraft, Iiiee Hawthorne Giilif, a oor-pmation of can-- Aspnaa tig t ga 5, Nbllialvza (o1.--24-4--ssi 90mins LQQThis invention .rlatefsj to controlsfdru'se 1n airplanes, ,and more particularly to ajmeans' and method Of regulating the rate. at which'the stick or,,contro1 column. of an-airplane can be'moved ifq -p l t-v s ce j A In an: airplane, having a vcontrol surf a'eefoper atedlwholly .by auxiliary Bowen; for; example, the pilots'eontrolstick .or cohimnsends' control. ig nals only to, theeQntrQI'surfaCe operating motors, and no aerodynamic forces acting on jtheycontrol surfaces, canlb'e felt'bynthe pilot. ln ila rge, highspeed airplanes having full IDOWQred control 'sur: faces, vthe pilot i can easily movegthe, stick; to

positions where the airplane. might( become greatly overloaded, even tq,destruetidn, partiou+ larly whenthe surface ismoved ineelevation con trolling directions. A} number l'of vdevices. have been: developed tomprevent1the. pil6t jrom lover,- leading such van airplane. -.AShKenas J 'Le am; pie, in applicationserial N0... 52,36,7Qfi1jd .Oct( 1b,er 1, 194a, nowabandoned,rderived aromermmgtne airstream .fiO-Wing past the airplane, andapplied that force ;.to center EhQ'COIItIZGLStiCK ,to providee, feel on the controls; when moved-away Inomnene tral, simulating. the aerodynamicforees aetingpn the ;contro1led-suriaces. 1..

A a F neyt i app a n se LNotfi fififi, le Jan r 8,1 me ur the rt a acc erations sacting. on the irpla ne,- andhapplied a fOKCBgtO' the stick varyin V to tend to move; the sticlgin zaxdirection tomedusee the ac l rat n: beine e e iene -a Qther, 555% tems (Feeney, application Serial No. 24,226, f i1ed April amid-1 8i h e:u ed,z e b natiq eeo aer dynamic; forces andsprings: towprovide! the. desired centering forcesh,

I Thexpresent ,ginvention i differs-z .iradica'll from any; of 4 the .-.afore'said adevicesgrin that: al-list-ick centeringforces are preferabiyfixed in value, but the rate. .at.-'=.which .ith':?StiCk :canrszbes movednis Placed under ethe controlaofiza forceuderivndirom airspeed,- or a forcederiyedlromivertiea-lraecelere ati'omcor: a =iorce-.::which is" a resultant of forces derived irhm bothairspeed "and vertiealaecelerae su'c ac e e at n byjthe piiojtj;inversely ,in aceordance with loads acting *on .saidairplane. a

It" is "'stiiliganoth'er object of the inventionto' prevent aerodynamic overloadinglof an airplane bygthe. airplane pilojt. h

Other objectst-and,advantages of the present inventionwi'll be apparent from theensuin'g'descriptio'n roithe appendedgdrfawings in which: .n

T'Figure 1 is aschemati'c diagram \of a preferred elevator -control system embodying. the .present invention. V

' Figure '2is alongitu'dinal sectional Tview of the rate'p'ontro'l"mechanism utilized in the systembf Figurel'. v l. The .control system shown in Figure l'ileomprisestheusualrbontrol stick.. l which; of course, is 'fii-lly "equivalentto a fcontrol column withia wheel or wheehsector for aileron :c'ontr'oL As-the device will be described as operating ondtheelefvae ter controls, "the: stick connections to'the ailerons arenot shown. a

Stick 1 i5?'CQ1II1EC1JEd,T for example, to operatea valvezibfahydraulie motor 3 of the-cylinder and pistdn'type,'"throu'gh "cable 4, the cylinder .of @the motor vbeing connectedlto anelevation control direction rand 1' amplitude'jof stick movement.

However; no forces actihgzon the elevatorwill be transmitted back to the pilot. The"rate' 'of sticlt'movement 'is' under the eon-- trotofa hydraulic assembly] 0 positioned 1702301; on'stic'k l ;*-thecylinder assemblybeing 'underth control of aforce measuring assembly Ill preferably-mounted" tin-hydraulic. assembly I 0 v "The hydraulic assemblyfi Bhomprisesa cylinder 4 2 through which a rod 1.! tpasses," this rod being eonn'ected'to Cable 'i by the use of couplings fl 5 on, each side'of'the cylinder, 12: Rod '1 f is sealed b'yqendrsealsyi 6 asjtpasses throughth' cylinder ends}: Cylinder"! Zjis divided into tvvmend imambersfi by a central internally extending ridge I9. The-rod, Withinth'e 'cylinder ha's a shoulder!!! formed thereon, a this shonlder,' when'the. stick'i islcentered; being in th'eplaneofcentral ridge l 9. Po'sitiomed"in each 'ich'amber I! and slideably mountedpn rod- I a is apiston2 I" havin anro'utward-1y extending shoulder 22" sealed by an 'OZl'ii'ig 23 w rod l 4 and seai'edxas by piston ringiZ Aitdthe interiorsurfabe 2 5 ofthe cylinder. iEabhpisto'n is adapted to" be picked- -'up and 'moved" outwardly only by shoulder 211' and isireturned inwardly by a centering spring '2 6 positioned inithe same; chain,

'braythepistonx In'the absence ofoth'r force's.

springs 26 will center the stick, and except for piloting forces applied directly to the stick by the pilot of the airplane, no other stick centering forces are provided.

However, the rate at which the istons 2| can be moved by the stick is under the control of the force measuring assembly H. I

This force measuring assembly comprises an assembly block 3|] mounted on cylinder l2 and supporting a pressure chamber 3|, closed by a cover 32. Mounted on cover 32 to extend into pressure chamber 3| is a flexible cylindrical bellows 34 closed inwardly by bellows plate 35 on which is mounted a Weight 36.

On the inner end of weight 36 and mounted centrally thereof, a valve rod 31 is extended, this valve rod being adjustable as to length with respect to weight by the use of nuts'39, so that valve rod 31 can be extended or retracted without turning the rod.

Valve rod 31 extends into the assembly block 30 to intersect a fluid duct 40. Fluid in this duct is isolated from pressure chamber 3| by seals 4| between valve rod 31 and the assembly block on each side of fluid duct 40.

The force measuring assembly H is positioned in the airplane with valve rod 31 vertical, when the longitudinal axis of the airplane is horizontal, so that movement of valve rod 31 by weight 36 will reflect vertical accelerations applied to the airplane.

The lower end of valve rod 31 enters'an equalizing cavity 42, this cavity being connected for pressure equalization to pressure chamber 3| by equalizing duct 44.

Balancing springs are provided bearing against end plate 46 on weight 36, the compression of these springs being under the control of adjustment screws 41 extending upwardly through the chamber 3| to support weight 36 against gravity and to control its position when the airplane is at rest. The restoring forces acting on weight 36 when the latter is displaced, can be distributed as desired between bellows 34 and springs 45.

Valve rod 31 is provided with a fluid bore 49 of substantially the same size as fluid duct 46 and registering therewith when the airplane is at rest, so that a free fluid path is provided through duct 40. One end of duct 40 is connected by cross duct 50 to cylinder |2, entering the cylinder centrally at the central ridge I9. The other end of duct 40 is connected to both ends of cylinder |2 through end pipe connection 52.

End pipe connection 52 is centrally connected to the interior of cylinder |2 through a bypass valve 53, which may be electrically operated through wires 53a by the pilot of the airplane, as by switch 54, conveniently located.

The hydraulic cylinder and connected piping is filled with hydraulic fluid through an inlet 55 and the hydraulic system also has attached thereto a temperature equalizer 56, as is well known in the art.

The interior of the bellows 34 is connected to line 6|] from the pitot head 59.

In operation of the device, the stick is normally centered by the forces exerted by springs 26,

4 so that as the stick is moved away from neutral, these forces will continue to act on the stick until the stick is again centered.

As the stick is moved away from neutral, one or the other of the pistons 2| will be picked up by shoulder 20 on rod l4 and will be moved outwardly in its respective chamber I1. This movement of a piston will cause fluid to flow through fluid duct 40 and the bore 49 in valve rod 31. When the bore coincides with the duct, free passage of the fluid from the end of the cylinder to the center of the cylinder is provided, and very little opposition to stick movement will be felt by the pilot. However, as airspeed increases, and assuming zero vertical acceleration, the bellows 34 will expand and will move valve rod 31 so that bore 49 and duct 40 no longer coincide and the flow of fluid through duct 40 will be restricted. This restriction will increase with increase in airspeed, thereby reducing the speed at which the control stick can be moved in the direction tending to increase airplane load factor. Movement of the stick in the opposite direction, i. e., with the shoulder 20 on rod |4 returning to central position in the cylinder, is not impeded as the rod |4 slides freely on the displaced piston, which is then returned to the central position by the associated compressed spring at the rate permitted by the position of valve rod 31. Thus, while the device resists movement of the stick in directions tending to increase airplane load factor, it does not resist movement of the stick in the opposite direction, nor is any pressure exerted on the stick when held stationary by the pilot, other than the pressure exerted by springs 26.

If desired, the maximum rate of movement of the stick can be controlled in accordance with airspeed alone, but as airplanes can be overloaded at moderate speeds by movement of controls which can cause large vertical accelerations to be imparted to the airplane, we prefer to also regulate the rate at which the stick can be moved in accordance with vertical acceleration. This action is provided by weight 36 which acts as an accelerometer mass to cause movement of valve rod 31 when the airplane is subjected to vertical accelerations, either positive or negative. The movement of the valve rod 31 will be in the direction reducing the rate at which the stick can be moved as acceleration increases, and again, will only restrict the rate of stick movement in the direction which would increase the acceleration.

In practical operation, the device can be set to impose a well defined resistance to movement of the stick in a direction tending to increase the loads on the airplane, when the loads are substantially equal to the design load factor of the airplane. The resistance to the stick movement can be made very large, for example, as the airplane loads approach 1.25 times the design load factor, and if desired can be made so high as to entirely prevent stick movement by the pilot in a direction to increase the load on the airplane when the airplane load approaches 1.5 times the design factor. At all times, the stick can be moved easily in the direction to reduce the load on the airplane.

As it is always possible that the device may function improperly or that certain conditions might obtain in a military emergency for example, where the stick should be freed from the resistance provided by the force measuring assembly, the emergency bypass valve 53 can be 7 control element, a cylinder adapted for holding a fluid, a central ridge in said cylinder extending internally from the cylinder bore, a rod movable with said control element entering said cylinder and having a central shoulder thereon smaller in diameter than the inner diameter of said ridge, a piston slidably mounted on said rod on each side of said shoulder, one of said pistons on each side of said ridge, the periphery of each of said pistons being sealed to the interior of said cylinder to prevent fluid flow therearound, elastic means in said cylinder and bearing against said pistons and the ends of said cylinder to urge said pistons toward said shoulder, a fluid duct between each end of said cylinder and a central point in said cylinder at said ridge between said pistons, and means for restricting fluid flow through said duct in accordance with a resultant of airspeed and vertical accelerations experienced by said airplane.

5. In an airplane having a control surface moved in accordance with movements of a pilots control element, a cylinder adapted for holding a fluid, a rod movable with said control element entering said cylinder and having a central shoulder thereon, a piston slidably mounted on said rod on each side of said shoulder, the periphery of each of said pistons being sealed to the interior of said cylinder to prevent fluid flow therearound, elastic means in said cylinder and bearing against said pistons and the ends of said cylinder to urge said pistons against said shoulder, and a fluid duct between each end of said cylinder and a central point, in said cylinder between said pistons, a weight resiliently mounted to move vertically in said airplane when said airplane is level, and a valve member attached to said weight and posi tioned to intersect said duct, said valve member having an aperture therein registering with said duct when said weight is at rest.

6. In an airplane having a control surface moved in accordance with movements of a pilots control element, a cylinder adapted for holding a fluid, a rod movable with said control element entering said cylinder and having a central shoulder thereon, a piston slidably mounted on said rod on each side of said shoulder, means preventing travel of each of said pistons, but not said shoulder, toward the other piston beyond a predetermined point in said cylinder, the periphery of each of said pistons being sealed to the interior of said cylinder to prevent fluid flow therearound, elastic means in said cylinder and bearing against said pistons and the ends of said cylinder to urge said pistons toward said shoulder, and a fluid duct between each end of said cylinder and a central point in said cylinder between said pistons, an element resiliently mounted to move in said airplane, a valve member attached to said element and positioned to intersect said duct, said valve member having an aperture therein registering with said duct when said element is at rest, and means for applying a differential pressure derived from the airstream flowing past said airplane to said element in a direction to move said element and said valve member.

7. Apparatus in accordance with claim 6 wherein. said valve member is positioned to move 8 vertically in said airplane when the latter is level, and wherein said element has sufflcient mass to move in response to vertical accelerations experienced by said airplane in flight.

8. In an airplane having a. control surface moved in accordance with movements of a pilots control element, a cylinder adapted for holding a fluid, a. rod movable with said control element entering said cylinder axially, a pair of pistons operating in said cylinder axially thereof, one of said pistons having acne-way driven connection with said rod in one direction and the other piston having a one-way driven connection with said rod in the other direction, elastic means in said cylinder and bearing against said pistons to urge said pistons in opposite directions, respectively, from their rod-driven directions, external fluid duct means between each end of said cylinder beyond each piston and a central point in said cylinder between said pistons, and variable means for restricting fluid flow through said duct means, whereby said restricting means can be controlled by an external control means.

9. In an airplane having a control surface moved in accordance with movements of a pilots control element, a cylinder adapted for holding a fluid, a rod movable with said control element entering said cylinder axially, a pair of pistons operating in said cylinder axially thereof, one of said pistons having a one-way driven connection with said rod in one direction and the other piston having a one-way driven connection with said rod in the other direction, elastic means in said cylinder and bearing against said pistons to urge said pistons in opposite directions, respectively, from their rod-driven directions, fluid duct means between each end of said cylinder beyond each piston and acentral point in said cylinder between said pistons, and means for restricting fluid flow through said duct means in proportion to an aerodynamic load on said airplane, wherein said fluid flow restricting means comprises an element resiliently mounted to move in said airplane, a valve member attached to said element and positioned to intersect said duct means, said valve member having an aperture therein registering with the flow passage of said duct means when said airplane is at rest, and means for applying a force representing said aerodynamic load to said element in a direction to move said element and said valve member to thereby regulate the now area of said duct means.

JOHN D. MoKELLAR. RONALD E. CRANDALL.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,828,383 Andersen Oct. 30, 1931 1,885,578 Boykow Nov. 1, 1932 FOREIGN PATENTS Number Country Date 321,851 Great Britain Dec. 3, 1928 449,431 France Jan. 30, 1913 569,290 Great Britain May 16, 1945 570,030 Great Britain June 19, 1945 

